Hi,
I have tried to implement all day now. The problem is, that the values
of the parent chartItem are populated by sqlalchemy after a flush. But
I would have to extract the value by the parent before a flush,
otherwise the db complains becuause sqllite would also try to flush
the child at the same time. I only see 2 ways out of this chicken /
egg dilemma:
1. Somehow implement the treelike self referential mapper directly in
the patient mapper (not in the patient.chartItem mapper) or
2. Do a huge tradeoff and sacrifice a clean db design so that only
patID or parent have values in child items.
I really hate option 2. So would it be possible to somehow implement
option 1?
Regards,
Hinrich Winther.
On 22.10.2008, at 19:43, Michael Bayer wrote:
>
> oh, ok. Here's a simplified case:
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
>
> engine = create_engine('sqlite:///:memory:', echo=False)
> Session = sessionmaker(bind=engine)
> session = Session()
> metadata = MetaData()
>
> # this table contains the base data for a patient, like his name,
> phone number ...
> patient_table = Table('patient', metadata,
> Column('patID', Integer, primary_key=True,
> nullable = False),
> Column('name', String),
> )
>
> # Stores data like which operations have been performed on a patient
> or which exams have been performed ...
> patientChart_table = Table('patientChart', metadata,
> Column('id', Integer, primary_key=True,
> nullable = False),
> Column('parent', Integer,
> ForeignKey('patientChart.id')),
> Column('type', String),
> Column('patID', Integer,
> ForeignKey('patient.patID'), nullable =
> False),
> )
>
> metadata.create_all(engine)
>
> class patient(object):
> pass
>
> class chartItem(object):
> pass
>
> mapper(chartItem, patientChart_table,
> properties={
> 'children': relation(chartItem)
> })
>
> mapper(patient, patient_table, properties={
> 'chart': relation(chartItem)
> })
>
> testpat = patient()
> testpat.name = "Test Patient"
>
> session.add(testpat)
> testpat.chart.append(chartItem())
> testpat.chart.append(chartItem())
>
> session.commit()
> print testpat.chart[0].id, testpat.chart[0].patID
> print testpat.chart[1].id, testpat.chart[1].patID
>
> c = chartItem()
>
> # there is no cascade from "patient" to the children of "chartItem"
> c.patID = testpat.chart[0].patID
> testpat.chart[0].children.append(c)
> session.commit()
>
> There is no cascade of patient's "patID" column to objects that are
> attached to its child "chart" objects, it only deals with the relation
> to the chart items that are immediately associated with it. You'd
> have to do that manually or add a before_save() hook to populate it.
>
> >
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